This invention relates to a method for constructing plaza decks or the like. A plaza deck is typically made up of a structural deck, a waterproof (non-permeable) membrane, an intervening foam insulation board, and a top concrete wearing slab. A known problem with this type of structure is a moisture build-up between the wear slab and the membrane This degrades the insulation value of the foam insulation board and can, and often does, cause freeze/thaw spalling of the cementicious wearing slab In order to alleviate the problems caused by moisture build-up between the wearing slab and the membrane, it is understood by the industry (and further supported by ASTM standard) that drainage is required (or at least recommended) between the insulation and the top covering. Some applications also include drainage between the membrane and the insulation. Drainage reduces the possibilities of moisture accumulation in the insulation (and therefore a reduction in thermal resistance) and moisture accumulation in the bottom side of the wear slab and, therefore, reducing the potential for freeze/thaw spalling.
With standard insulation products currently being used in plaza deck construction, the drainage layer usually consists of loose gravel or epoxy bound gravel. This drainage layer is often covered with a layer of construction fabric which is then covered with poured concrete or a preformed concrete panel. The labor and material costs associated with installation of such a gravel layer above or above and below the membrane are significant because loose gravel and/or epoxy bound gravel require considerable handling expertise in order for them to be transported to the job site, and these materials require intensive labor to be applied. Further, the gravel layer adds weight necessitating structural considerations and height which is often limited in reroof situations causing detailing difficulties.
Ways to avoid the installation of loose gravel or epoxy bound gravel as the drainage layers in these protected membrane roofing structures were recited in U.S. Pat. Nos. 4,658,554 and 4,712,349. In both of these patents, the insulation layer itself provides the necessary drainage in that the insulation is a type of foamed plastic that is sculpted such that its top surface is made up of elongated ribs arrayed, with cut-out channels interposed between them, with the walls surrounding the channels demarking the ribs. This channel/rib construction provides for drainage of moisture that accumulates between the insulation panels and wearing slabs. In both of these patents all of the insulation panels have a plastic film laminated to the lower surface of the insulation panel such that the plastic film prevents migration of moisture vapor through the insulation to the insulation wearing slab interface from the waterproof membrane. This type of dual moisture retarder and drain-away system provides for adequate drainage in these types of roofing structures.
The disadvantage of the methods outlined in the '554 and the '349 patent is that in both methods, in order to finish the roofing structure, concrete panels have to be laid directly on top of the polystyrene foam. Because the concrete panels have to be laid directly on top of the foam, this means that these concrete panels have to be created in one location, then transported to the job site, and at the job site the panels have to be lifted to the working area, wherever it may be--the roof--or various levels of a parking structure. As is well known, the transportation of extremely heavy, unbalanced concrete slabs is difficult, time consuming and extremely expensive, both from a materials standpoint and a labor standpoint. Further, a top covering comprised of preformed wearing slabs is typically not appropriate for loads heavier than pedestrian traffic. For loads like vehicle traffic monolithic wearing slabs are needed to adequately distribute loads and prevent damage to the underlying insulation layer.